Application for British nationality

The rules for British nationality for adults is by way of naturalisation. 
You can apply for British citizenship by naturalisation if:
You’re 18 or over

You are of Good Character

You’ll continue to live in the UK

You’ve met the knowledge of English and life in the UK requirements

You meet the residency requirement
And you must usually have:

• lived in the UK for at least the 5 years before the date of your application
• spent no more than 450 days outside the UK during those 5 years
• spent no more than 90 days outside the UK in the last 12 months
• had settlement (‘indefinite leave to remain’) in the UK for the last 12 months. If you are from outside the European Economic Area (EEA), you must have held permanent residence status for the last 12 months. You will need to provide a permanent residence document
• not broken any immigration laws while in the UK

If you are married to a spouse or civil partner is a British citizen.
You may apply after 3 years if you have obtained Indefinite Leave to remain, if you have been married during this time, provided the other requirements are met.
You will not be able to rely upon the time if you have been exempt from immigration control (for example, as a diplomat or member of visiting armed forces) as part of the 3 or 5 years.

Children 
Those under the age of 18 may apply for registration if they satisfy the Immigration rules. Children born abroad or those who are abroad and applying for their First British Passport, will have to send their application to the Her Majesty’s Passport Office in Belfast.